Trimming File Size

I’m up against a 5 MB file size for a song. I exported as MP3 with a sample rate of 11,025 Hz, 16 bit, fast sync interpolation in an older version of Audacity. It resulted in a file size of about 5.2 MB

I just upgraded to version 2.3.3 and tried again. I set it to a sample rate of 8,000 Hz, 16 bit, low quality. But now I get a nearly 8MB file size. Is there anyway to get the file size further reduced without clipping off part of the song?

What’s the playing time of the song?

Choose a lower bit rate (kbps). The bitrate is kilo_bits_ per second and there are 8-bits in a byte so you can divide by 8 to get the file size in kilo_bytes_ per second.

…The sample rate (11,050Hz or 8,000Hz) has a direct correlation to uncompressed file size, but NOT with MP3… i.e. 8000Hz, 16-bit, stereo, uncompressed is 8kHz x (16/8) x 2 = 32 kilobytes per second. (Or a bit rate of 256kbps)

11,025 Hz & 8,000 Hz sample-rates are too low for music: it will sound like it’s over the phone.
Go back to the original 44100Hz and use the lowest mp3 bit-rate necessary to get the size you need…
https ://
(use mono if you don’t need stereo).

(use mono if you don’t need stereo).

What he said. Mono (one blue wave) is a good way to slash file sizes and it may get slashed so much you can push the overall quality and sampling rates back up.


Do you have to use MP3 or do you have to meet the 5MB filesize? MP3 is part of a video format designed in 1990. There’s better sound formats now.


Thanks! That did it! I absolutely do not need stereo for this. Switching to mono brought it down to under four minutes. Ideal.
Thanks again!

The 5 MB file size was the constraint. I have to admit to not being familiar with other audio file types (other than WAV). I’ve solved it my exporting as mono. Where can I learn about the there file types you speak of?

“Lossless” formats (such as WAV and AIFF) generally have about the same file size that can be calculated by multiplying:
bits per sample x samples per second x number of channels x time (in seconds)
To get the figure in bytes, divide by 8.
1 kilobyte = 1000 bytes, so for kB, divide by 8000

Thus for CD audio, there are 16 bits per sample, 44100 samples per second, 2 channels:
16 x 44100 x 2 = 1411200 bits per second (1411.2 kbps) = 176.4 kB per second
So a 1 hour recording will have 635040 kB of data = 635.04 MB

FLAC is also a “lossless” format, but it has a special way of squashing the data together to reduce the file size. A Flac file is typically around 40% smaller than a WAV file. Flac supports 16 bits per sample or 24 bits per sample. 16-bit Flac is more common, and a 1 hour CD quality Flac file will typically be around 400 MB in size.

“Lossy” formats (sometimes, though less accurately called “compressed” formats) achieve much smaller file size by discarding some of the audio data. This inevitably leads to some loss in sound quality, but the quality is generally MUCH better than reducing the bits per sample or samples per second of a lossless format. Lossy formats are the ideal choice when small file size is the primary consideration.

MP3 is the most common lossy audio format. It is very widely supported. Reasonably good quality stereo music can be achieved at 128 kbps. Note that this is massively less than the 1411.2 kbps for CD quality WAV. Higher “kbps” give better quality at the expense of larger file size.
For equivalent quality mono recordings, the “kbps” can be reduced by about half. Thus for reasonable quality mono music, 64 kbps is a good choice.

OGG is a more recent format than MP3, and is generally considered to be better than MP3, though it is less widely supported that MP3.

Opus is a relatively new format and is arguably the best general purpose lossy format that exists. It is less widely known than MP3 or OGG, but it is supported by all modern mainstream web browsers. At 128 kbps the quality for stereo music is excellent. For mono speech recordings, the bit rate can be brought down close to 6 kbps with “better than telephone” quality.

There are numerous closed source “proprietary” formats, such as Apple’s “AAC” and Microsoft’s “WMA”. These formats are generally in the same ballpark as MP3 and OGG when it comes to the quality / file size trade off for music. In most cases they are designed to give very good quality for stereo music at around 160 kbps.

Wow, thanks, Steve. I had no idea there were so many choices. I’ll have to play around with one or two of them.